When you put mouse cursor over node, it will mark direct child nodes with

When you click on node, all child nodes (even indirect) will be hidden, and the node you clicked on will be marked with

Both features are directed towards people who analyze longer plans – ability to hide parts or just visually see what the Nested Loop is calling in 2nd stage greatly helps me see the flow of query – you can test it, for example, here.

By the way – BIG THANK YOU for Metys for help on it (well, actually, for doing it).